1. Field of the Invention
The present invention relates to a laminated inductor, and more particularly, to a laminated inductor structured to improve direct current (DC) bias characteristics.
2. Description of the Related Art
Conventionally, a direct current/direct current (DC/DC) converter used as a major power source for a personal computer and mobile devices has mainly adopted a transformer or choke coil having a coil wound around a magnetic core. However, recently, with the demand for a smaller and thinner product, a laminated inductor, which is a chip part of a laminated structure, has been commercially viable.
A general laminated inductor has a structure such that a plurality of magnetic layers each having conductor patterns thereon are laminated. The conductor patterns are sequentially connected by a conductive via formed in each of the magnetic layers and overlapped in a laminated direction to thereby form a spiral-structured coil. Moreover, the coil has both ends drawn out to an outer surface of a laminated body to be connected to external terminals, respectively.
As described above, the laminated inductor has a coil surrounded by a magnetic body and thus experiences less magnetic flux leakage. Also, the laminated inductor can be beneficially reduced in size and thickness due to its laminated chip structure.
However, despite these advantages, the laminated inductor for use in a power circuit such as a DC/DC converter undergoes a sharp decrease in inductance, or degraded in DC bias characteristics owing to magnetic saturation of the magnetic body. Therefore, studies for preventing such a rapid decline in inductance have been conducted.
U.S. Pat. No. 6,515,568 and Japanese Patent Laid-Open Publication No. 2006-318946 disclose conventional methods for improving DC bias characteristics. By these methods, a magnetic substance with a low magnetic permeability or non-magnetic substance is inserted into a chip to delay magnetic saturation of a magnetic body.
According to the conventional technologies, layers where conductor patterns are formed are partially substituted by electrically insulating non-magnetic layers, or a portion of a corresponding layer is formed of an electrically insulating non-magnetic material.
However, these methods require more materials to be utilized due to selection of a heterogeneous non-magnetic material and entail a subsequent additional process cumbersomely. Notably, when a portion of the corresponding layer is substituted, a process of laminating sheets is considerably complicated.
Besides, conventionally, a heterogeneous material of non-magnetic layer is intercalated between the magnetic layers mainly constituting an inductor body. Therefore, the non-magnetic layer may be detached from other layers during firing due to differences in a shrinkage ratio.